To calculate the theoretical amount of solder paste that will be used for each board, the weight of solder paste for each aperture on the board will need to be calculated. Once all of the weights have been calculated they can be added together which will result in the amount of solder paste per board.

Of course this is the theoretical value and not an actual value. The easiest way to determine the actual paste weight per board is to weigh a board before the paste has been printed and then again after the paste has been printed. The difference is the actual solder paste weight or consumption of solder paste per board. Of course, there will be some margin of error even in this calculation due to the weight tolerances of the board and the variations in solder paste deposits from print to print.

Let me know if I can help you calculate or estimate the amount of solder paste your project will consume.
Chris